a) Field of the Invention
The present invention relates to an automatic load matching circuit for microwaves in various transmission lines such as, for example, waveguides, coaxial tubes, and so forth. More particularly, it is concerned with an automatic load matching circuit for microwaves using a multi-element matching device.
b) Description of Prior Arts
Industries require a particularly stable source of energy for the sake of the best possible quality control of their products. Adoption of microwave power as the source of energy in various industrial facilities exhibits, in many cases, a special effect in comparison with adoption of other sources of energy, hence its effective utilization has been much expected. Such microwave electric power, however, has a very wide range of fluctuations, and yet its fluctuations often take place abruptly. It has been particularly desirable that such microwave power be supplied stably during operation of the production facilities to achieve the best quality control, for which the so-called "load-matching" has been carried out.
Heretofore, the load-matching in the microwave band has been done by manual operations of three or more stubmatching devices, E/H matching devices, and so on, while monitoring the travelling wave power to a load as well as the reflected power from the load, to thereby adjust the load to the maximum point of the travelling wave power with the minimum reflected power.
With the manual load-matching operation as described above, however, it is necessary that such fluctuations in the load constantly be monitored so as to effect prompt operation in response to the fluctuations, hence such quick and accurate response to the abrupt fluctuations in the load is very difficult. Due to this difficulty, there has been a problem in the quality control such that delay occurs in taking appropriate response at the abrupt change in the load conditions.
In view of this, the present inventor has previously proposed an automatic load-matching circuit for microwaves which carries out automatic load-matching as mentioned above, as disclosed in published Japanese Patent Document No. 63-15502 with which the intended purpose has been met for the time being, although there still remained a difficulty, among others in that a zone of no matching still existed.
After the abovementioned proposal on the automatic load-matching circuit for microwaves, there followed improved circuits, in which E/H matching devices were utilized as disclosed in published Japanese Patent Document No. 63-264892 and No. 63-264893. These circuits, however, also had a disadvantage in that the circuit construction was somewhat complicated.